The present invention relates to a member or guide for infrared ray transmission, such as optical fibers, which well transmit infrared rays of 2 .mu.m or longer in wavelength, and particularly to a member for infrared ray transmission capable of transmitting infrared rays of 10.6 .mu.m in wavelength with a small loss.
In recent years, optical fibers capable of transmitting of about 10.6 .mu.m in wavelength have been demanded for a CO.sub.2 -laser beam guide or infrared ray guide for a radiation thermometer. Various materials have been investigated for meeting the demand, the fibers of TlBr-TlI were found to transmit a ray of 10.6 .mu.m in wavelength with a slight loss of 0.4 dB/m (Sakuragi et al., O plus E, published by Seiki Tsushinsha, October, 1980, pp. 49-53). However, it has been revealed that these fibers, because of the polycrystalline structure thereof, has the drawbacks of being brittle and exhibiting an increased light scattering loss due to the plastic deformation thereof caused by bending.
Se- or S-containing chalcogenide glass fibers are free of the same drawbacks as those of the fibers of TlBr-TlI, but is deficient in practicality since the transmission loss of a ray of 10.6 .mu.m in wavelength is as great as 4.5 dB/m (S. Takahashi et al., Technical Digest of 100 C, 1983, Tokyo 30A 2-4).